Electron tube



Dec. 22, 1959 w, w, rr ET AL 2,918,597

ELECTRON TUBE Filed Feb. 23; 1956 IN V EN TORS Will/am W. E/fe/ Jack A.M. Cu//oug/1 Geo/ye f? Wander/1th BYM CAP ATTORNEY United States Patent"ice ELECTRON TUBE William W. Eitel, Woodside, Jack A. McCullough,Millbrae, and George F. Wunderlich, Burlingame, Calif., assignors toEitel-McCullough, Inc., San Bruno, Calif., a corporation of CaliforniaApplication February 23, 1956, Serial No. 567,129

Claims. (Cl. 313---242) This invention relates to electron tubes andmore particularly to improvements in internal shielding structures andcathode supporting structures.

An important requirement for electron tubes is that they have a longlife. As is well known by those skilled in the art, there is a tendencyfor the glass or other insulating material in the tube envelope todeteriorate under the influence of heat and bombardment by electrons andions, so that after a period of time the insulating material is weakenedto the extent that it admits air to destroy the tube vacuum. 1

Accordingly, an object of the invention is to provide an improvedshielding arrangement for protecting the insulating material in the tubeenvelope from the destructive effects of heat and bombardment byelectrons and 10118.

An additional object is to provide an electrostatic shieldingarrangement for protecting the insulating material in the tube envelopefrom bombardment by electrons and 10118.

A further object of the invention is to provide a tube of the typedescribed having an improved arrangement for supporting a cylindricalcathode.

Another object is to provide in conjunction with the improved cathodesupport an improved terminal arrangement whereby the cathode support andthe terminals are grouped compactly around the tube axis so as not tointerfere with the positioning of the shielding structure.

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be set forth in the followingdescription of the invention. It is to be understood that the inventionis not limited to the disclosed species, as variant embodiments thereofare contemplated and may be adopted within the scope of the claims.

Referring to the drawings:

Figure 1 is essentially a vertical sectional view on the center line ofa diode embodying the improvements of the invention and shows a portionof the lower end of the tube in elevation.

Figure 2 is a bottom view of the improved tube; and,

Figure 3 is a sectional view taken on the line 33 of Figure 1.

Referring in more detail to the drawings, it will be seen that the tubecomprises a header 2 of insulating material such as glass forming thebottom of the tube envelope. A side section 3 of the envelope ispositioned above the header and is also made of insulating material suchas glass. The upper end of the envelope is formed by an external anode 4in the shape of a cup inverted above side section 3. The header 2 isjoined to the side section 3 by means of a sealing ringunit 5 which ismade up of a lower metal ring 6 and an upper metal ring 7. The inneredge of ring 6 is sealed in the header 2, and the inner edge of ring 7is sealed in the lower end of side section 3. The rings 6 and 7 areshaped so that their outer edges are in contact, and these edges arejoined by a weld indicated at 8. Anode 4 is joined to the side PatentedDec. 22, 1959 section 3 by means of a metal ring 10 having its outeredge sealed in the upper end of side section 3 and its inner rim brazedto the side of anode 4. The top of the anode is provided with an exhausttube 11 which is pinched off in the usual manner. In order to dissipateheat from the anode, it is provided with cooling fins 12. Each of thefins 12 is generally channel-shaped in cross section to form an innertab 13 and an outer tab 14. The fins are secured in place by solderingthe inner tabs 13 to the anode as indicated at 15 in Figure 1.

A plurality of terminal pins 17, 18, 19 and are sealed in header 2. Pins17 and 18 serve as leads for a getter 21. Pin 19 serves as a support fora cylindrical cathode unit 23 and for this purpose is extended upwardlyand bent inwardly so that its upper end is coaxially positioned withinthe tube. At the upper end of cathode unit 23 is the actual cathodecylinder 24. The

side walls of cylinder 24 form the emitting surface, which -ispreferably of the oxide coated type. A thin ring 25 of material such askovar is brazed to the bottom of cylinder 24 to act as a heat dam, and atubular metal skirt 26 is brazed to the bottom of ring 25. A bottompiece 27 is brazed to the end of skirt 26, and the upper end of terminalpin 19 is brazed to the bottom piece to support the entire cathode unit.The cathode is pro vided with a heater coil 28 having its upper end 29spot welded to the top of cathode cylinder 24. The lower end 30 of theheater coil is extended downwardly through an insulating plug 31 andspot welded to terminal pin 20. The heater coils 28 are coated in theusual manner with insulating material to prevent electrical contact withcathode cylinder 24. It will be seen that with the described arrangementpin 19 serves as a terminal for both the cathode and one end of theheater, the other end of the heater being served by pin 20.

The improved shielding structure is formed partly by anode 4, which isextended downwardly at 33 into the tube to a point well below the lowerend of cathode cylinder 24 and the upper end of side section 3. Thereare several reasons for this arrangement, one being to prevent straightline travel of electrons from any point on the cathode to any point onthe side section 3. Another reason is to prevent heat radiation from thehot cathode structure to the side section 3, particularly at the sealbetween the upper end of the side section and ring 10. Thus, a majorportion of the radiant heat which would normally strike side section 3will be picked up on the anode extensions 33 and dissipated through fins12.

In order to complete the arrangement for shielding side section 3 fromheat and bombardment by stray electrons and ions, a lower metalshielding ring 34 is provided. It will be seen that by using the pintype terminals 17-20 and the pin type cathode support, shielding ring 34can be spaced around all of these elements and yet have a relativelysmall diameter which is substantially equal to the diameter of. anodeextension 33. An outwardly extending metal flange 35 is brazed orotherwise attached to the bottom of shield 34 with the periphery offlange 35 being clamped between the metal rings 6 and 7. In this mannerthe sealing ring unit 5 serves as a terminal for shield 34, and theshield is completely insulated from all of the tube electrodes. Thus,the shield 34 may be connected to a voltage having a relatively lowvalue compared with that of the anode so that a voltage gradient can beestab ished across the annular gap between the upper end of shield 34and the lower end of the anode extens on 33. Thus, the shieldingelements 33 and 34 not only form a physical barrier throughout theirlengths, but by virtue of the voltage grad ent form an electrostatictrap which further prevents passage of electrons and ions outwardly tothe side section 3. As stray electrons and ions attempt to pass throughthe electrostatic field between shielding elements 33 and 34, theelectrons will be deflected toward the shielding element which forms themore positive side of the field, and the ions will be deflected towardthe shielding element which forms the less positive side of the field.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. An electron tube comprising an anode, a cathode, a metal shield andinsulating means separating said shield from said anode and cathode,said shield being positioned in the tube so as to prevent direct passageof electrons from said cathode to said insulating means, said shieldhaving one end axially spaced from said anode and having a diameter atleast equal to said anode to form within the tube a gap between saidanode and said shield, and a terminal for said shield projecting outsideof the tube whereby an electrostatic field may be established acrosssaid gap.

2. An electron tube comprising a plurality of electrodes, including ananode and a cathode, an envelope for said tube comprising a side sectionof insulating material, said anode being cup-shaped and inverted oversaid side sec tion to form the upper portion of said envelope, meanssealing said anode to the upper end of said side section, a metalshielding ring positioned below said anode and having a diameter atleast equal to the inner diameter of said anode to form an annular gapbetween the upper end of said ring and the lower end of said anode toprevent direct passage of electrons from said cathode to said sidesection, insulating means including said side section separating saidshield from all of said electrodes, and a terminal for said shieldprojecting out of the envelope whereby an electrostatic field may beestablished across said gap.

3. An electron tube comprising a plurality of electrodes including acathode and an anode, an envelope for said tube comprising a sidesection of insulating material and a header of insulating material, ametal sealing ring unit joining said header to said side section, and ametal shielding ring inside the envelope and terminating adjacent saidanode to form a gap between the anode and shielding ring, said shieldingring being connected to said sealing ring unit and insulated from all ofsaid plurality of electrodes, said metal shielding ring having an insidediameter at least equal to the inside diameter of said anode whereinsaid metal shield prevents the direct passage of electrons from saidcathode to said side section, whereby said sealing ring unit serves as aterminal for said shielding ring and an electrostatic field may beestablished across said gap.

4. An electron tube comprising an envelope having a header of insulatingmaterial at the lower end, a side section of insulating materialpositioned above said header, and a cup-shaped anode inverted above saidside section and forming the upper end of the envelope, a cathodepositioned within said anode, means joining said anode and the upper endof said side section, the side walls of said anode projecting downwardlya substantial distance below the upper end of said side section andspaced inwardly therefrom, ,a sealing ring unit joining said header andthe lower end of said side section, said ring unit comprising a firstmetal ring having one end sealed in said header and extending outwardlytherefrom, said ring unit further comprising a second metal ring havingone end sealed in said side section and "extending outwardly therefrom,a metallic bond joining the outer ends of said first and second rings, agenerally cylindrical metal shield positioned within the lower end ofsaid side section and spaced from said anode, said shield having aninner diamter at least equal to the inner diameter of .said anodewherein said shield prevents the direct passage of electrons from saidcathode to said side section, said shield having an outwardly extendingmetal flange at its lower end, the outer portion of .said .fiange beingsecured between said first and second rings whereby said ring unitserves as a terminal for said shield so that an electrostatic field maybe established across the space between said anode and .said shield, andsupportingmeansforssa'id cathode positioned within'said shielding ring.

5. An electron tube comprising an envelope having a header of insulatingmaterial at the lower end, a side section of insulating materialpositioned above said header, and a cup-shaped anode inverted above saidside section and forming the upper end of the envelope, means connectingsaid anode to the upper end of said :side

section, a connecting ring unit joining said header and the lower end ofsaid side section, said ring unit comprising a firstmetal ring havingone end joined to said header and extending outwardly therefrom, saidring unit further comprising a secondmetal ring having one end joined tosaid side section and extending outwardly therefrom, a metallic bondjoining the outer ends of said first and second rings, a generallycylindrical metal shield positioned within the lower end of said. sidesection and spaced inwardly therefrom, said shield having an outwardlyextending flange at its lower end, the outer portion of said flangebeing secured between said first and second rings, the upper end of saidshield terminating adjacent the lower end of said anode, said shieldhaving an inner diameter at least equal to the inner diameter of saidanode wherein said shield is positioned to prevent direct passage ofelectrons from said cathode to said side section, a cylindrical cathodeand a heater for the cathode both positioned concentrically within saidcup-shaped anode, terminal pins for said cathode and heater sealed insaid header radially inwardly of said shield and projecting downwardlyout of the envelope, one of said pins extending upwardly into saidanode, and means supporting .said cathode on the upper end of said onepin.

References Cited in the file of this patent UNITED STATES PATENTS1,929,369 Found Oct. 3, 1933 2,236,859 Vandegrift Apr. 1, 1941'2,471,005 Norton -a May 2-4, 1949 2,644,907 Drieschman et al July 7,1953 2,726,346 Busby et al Dec. 6, 1955 2,727,178 Dailey-et al Dec. 13,1955

